JP2011023473A - Group iii nitride semiconductor laser diode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a stable oscillation mode while suppressing a deterioration in crystal quality of an active layer in a long-wavelength group III nitride semiconductor laser diode formed on a semi-polar primary surface. <P>SOLUTION: The group III nitride semiconductor laser diode 11 includes a group III nitride substrate 13 having a semi-polar primary surface 13a, an n-type cladding layer 15 made from aluminum-containing group III nitride, the active layer 17, a p-type cladding layer 19 made from aluminum-containing group III nitride, an optical guiding layer 21 provided between the n-type cladding layer 15 and the active layer 17, and an optical guiding layer 23 provided between the p-type cladding layer 19 and the active layer 17. The optical guiding layers 21 and 23 composed of first layers 31, 35 made from GaN and second layers 33 and 37 made from InGaN, and the total thickness of the first respective optical guiding layers 21 and 23 is greater than 0.1 [μm]. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a group III nitride semiconductor laser diode.

  Patent Document 1 describes a Fabry-Perot type semiconductor laser diode having an oscillation wavelength of 500 [nm] or more. In this semiconductor laser diode, an n-type semiconductor layer, a light emitting layer, and a p-type semiconductor layer are stacked on a GaN substrate having a nonpolar plane (m-plane) as a main surface. The n-type semiconductor layer includes an n-type GaN cladding layer and an n-type InGaN light guide layer. The p-type semiconductor layer includes a p-type GaN cladding layer and a p-type InGaN light guide layer.

  Patent Document 2 describes a laser element having an oscillation wavelength of 425 [nm] to 450 [nm]. In this laser element, an n-type GaN clad layer, an active layer, and a p-type clad layer are laminated on a GaN substrate having a c-plane as a main surface, and between the n-type clad layer and the active layer, and the p-type A GaN light guide layer is provided between the cladding layer and the active layer, and a nitride semiconductor layer containing In is further provided between the GaN light guide layer and the active layer.

JP 2008-31640 A JP 2002-270971 A

  A laser diode using a group III nitride semiconductor is a candidate for realizing a laser diode having a long wavelength such as an oscillation wavelength of about 500 [nm]. In such a long wavelength laser diode, a group III nitride semiconductor containing In is used as an active layer, and a group III nitride semiconductor containing In is used to stably confine light in the vicinity of the active layer. A light guide layer made of is provided above and below the active layer.

  In order to obtain a stable oscillation mode at a long wavelength of about 500 [nm], for example, a thick light guide layer exceeding a thickness of 100 [nm] is required. However, when a light guide layer made of a group III nitride semiconductor containing In is grown thickly on, for example, a GaN substrate, the crystal thickness of the active layer is lowered because it approaches the critical film thickness. In particular, when the crystal growth surface of the substrate is a semipolar surface, the c-plane acts as a sliding surface, and the crystal quality of the active layer is significantly reduced. Further, in order to increase the optical confinement factor (Γwell), it is necessary to increase the In composition of the light guide layer, thereby further reducing the crystal quality of the active layer.

  In the laser element described in Patent Document 2, since an InGaN active layer or the like is grown on a GaN substrate having a c-plane as a main surface, an In composition that can generate light having a long wavelength of 500 [nm]. In this case, the luminous efficiency is lowered by the piezoelectric field caused by the difference in lattice constant, and it is difficult to obtain a practical laser diode having a long wavelength.

  The present invention has been made in view of such problems, and suppresses deterioration of the crystal quality of the active layer in a long-wavelength group III nitride semiconductor laser diode formed on a semipolar main surface. However, an object is to obtain a stable oscillation mode.

In order to solve the above-described problem, a group III nitride semiconductor laser diode according to the present invention is a group III nitride semiconductor laser diode that outputs laser light having a wavelength of 480 [nm] or more and 550 [nm] or less, A group III nitride substrate having a semipolar main surface, a first conductivity type first cladding layer made of a group III nitride containing Al and provided on the group III nitride substrate, and a first cladding layer; An active layer provided, a second cladding layer of a second conductivity type provided on the active layer and made of a group III nitride containing Al, between the first cladding layer and the active layer, and the second cladding layer A light guide layer provided between at least one of the first layer and the active layer, wherein the light guide layer includes a _first layer made of In _x1 Ga _1-x1 N (0 ≦ x1 <1), In _x2 Ga _1-x2 provided between the active layer and the active layer N (x1 <x2 <1), and the total thickness of the first and second layers is greater than 0.1 [μm].

  In a group III nitride semiconductor laser diode having an oscillation wavelength of 480 [nm] or more and 550 [nm] or less, the refractive index is relatively high in order to obtain a stable oscillation mode by strongly confining light near the active layer. It is effective to use InGaN for the light guide layer. However, when the light guide layer containing InGaN is thickened, there is a problem that the crystal quality of the active layer is significantly deteriorated as described above.

  Therefore, in the group III nitride semiconductor laser diode described above, the light guide layer includes the first and second layers, and the In composition x2 of the second layer located on the active layer side is the first layer. It is higher than the In composition x1. Thus, by providing two layers having different In compositions in the light guide layer, the second layer having a high In composition in the vicinity of the active layer enhances the light confinement action, and the first In composition has a low In composition. The layer can increase the thickness of the light guide layer while suppressing the deterioration of the crystal quality of the active layer. Therefore, a stable oscillation mode can be obtained by the light guide layer having a thickness larger than 0.1 [μm]. In addition, this effect is particularly remarkable when a group III nitride substrate having a semipolar main surface is used.

  In the group III nitride semiconductor laser diode, the light guide layer is provided at least between the second cladding layer and the active layer, and the light guide layer provided between the second cladding layer and the active layer is provided. An electronic block layer provided so as to be divided in two in the layer thickness direction may be further provided. In this case, the distance between the electron blocking layer and the active layer is preferably 50 [nm] or more.

  In the group III nitride semiconductor laser diode described above, the main surface of the group III nitride substrate is a semipolar surface. In the laser diode structure formed on the semipolar plane (particularly on the semipolar plane where the piezoelectric field is negative), electrons hardly leak to the p-type semiconductor side. Therefore, the distance between the electron blocking layer and the active layer can be increased to 50 [nm] or more, which is difficult on the c-plane or nonpolar plane (m-plane). As a result, it is possible to prevent the light emission characteristics from being deteriorated due to the electron blocking layer distorting the active layer. Further, by widening the distance between the electron blocking layer and the active layer to 50 [nm] or more, the shift of the electric field distribution toward the n-type semiconductor side can be prevented, and the oscillation threshold can be effectively reduced.

  The group III nitride semiconductor laser diode may be characterized in that the total thickness of the first and second layers is smaller than 0.5 [μm]. As a result, the optical confinement factor (Γwell) is increased, and laser oscillation can be suitably realized.

  The group III nitride semiconductor laser diode may be characterized in that the In composition x2 of the second layer satisfies 0.01 ≦ x2 ≦ 0.1. When the In composition x2 is 0.01 or more, a sufficient refractive index is ensured, the optical confinement coefficient (Γwell) is increased, and laser oscillation can be suitably realized. Further, when the In composition is 0.1 or less, the crystal quality of the active layer can be maintained high, and the light emission efficiency can be improved.

の関係を満たすことを特徴としてもよい。第２の層の厚さｄ２がこのような関係を満たすことによって、活性層の結晶品質の低下を効果的に抑制し、十分な発光効率を得ることができる。 Further, in the group III nitride semiconductor laser diode, the thickness d2 [nm] of the second layer is

It may be characterized by satisfying this relationship. When the thickness d2 of the second layer satisfies such a relationship, a decrease in crystal quality of the active layer can be effectively suppressed and sufficient luminous efficiency can be obtained.

Furthermore, III-nitride semiconductor laser diode, III-nitride substrate is made of _{In S Al T Ga 1-S} -T N (0 ≦ S ≦ 1,0 ≦ T ≦ 1,0 ≦ S + T ≦ 1), the main surface of the group III nitride substrate is inclined at an angle of the _{in S Al T Ga 1-S} -T N {0001} plane or the {000-1} range of less than 10 degrees than 90 degrees the surface as a reference crystal It is good also as a feature. The angle of the case, the principal plane of the Group III nitride _{substrate, In S Al T Ga 1-} S-T N {0001} plane or the {000-1} range of less than 80 degrees 63 degrees or more relative to the surface of the crystal It is still more preferable that it is inclined at.

  The group III nitride semiconductor laser diode may be characterized in that the group III nitride substrate is made of GaN. This enables epitaxial growth with good crystal quality.

Further, the group III nitride semiconductor laser diode may be characterized in that the principal plane of the Group III nitride substrate is inclined in the m-axis direction of _{In S Al T Ga 1-S} -T N crystals. Thereby, the incorporation efficiency of In when growing the light guide layer and the active layer is increased, and as a result, good light emission characteristics can be obtained.

  According to the present invention, in a long-wavelength group III nitride semiconductor laser diode formed on a semipolar main surface, a stable oscillation mode can be obtained while suppressing a decrease in crystal quality of the active layer. .

FIG. 1A is a drawing schematically showing the structure of a group III nitride semiconductor laser diode according to a first embodiment of the present invention. FIG. 1B is an enlarged view showing a part of the configuration of the active layer 17 having a quantum well structure. FIG. 2 shows a growth temperature [° C.], a growth rate [Å / min], a flow rate of TMGa [μmol / min], and a flow rate of TMIn in one embodiment of the method for manufacturing the group III nitride semiconductor laser diode 11. 6 is a chart showing [μmol / min], TMAl flow rate [μmol / min], and NH ₃ flow rate [slm (standard liter / min)]. FIG. 3 shows an experiment to determine whether good laser oscillation can be obtained by changing the In composition x2 and the thickness of the second layers 33 and 37 of the light guide layers 21 and 23 (whether the light emission efficiency is sufficient). It is a graph which shows the result investigated by (1). FIG. 4 is a drawing schematically showing the structure of the group III nitride semiconductor laser diode 12 according to the second embodiment. It is a graph which shows the result of having calculated the light confinement coefficient Γwell by changing the thickness of the light guide layers 21 and 25. FIG. 6A to FIG. 6C show the distribution of guided light when the oscillation wavelength is changed in the group III nitride semiconductor laser diode 12 having an optical waveguide layer thickness of 390 [nm]. It is a graph. FIGS. 7A to 7C show the distribution of guided light when the oscillation wavelength is changed in the group III nitride semiconductor laser diode 12 having an optical waveguide layer thickness of 490 [nm]. It is a graph. FIGS. 8A to 8C show the distribution of the guided light when the oscillation wavelength is changed in the group III nitride semiconductor laser diode 12 whose optical waveguide layer has a thickness of 590 [nm]. It is a graph.

  Embodiments of a group III nitride semiconductor laser diode according to the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

(First embodiment)
FIG. 1A is a drawing schematically showing the structure of a group III nitride semiconductor laser diode according to a first embodiment of the present invention. A gain guide type III-nitride semiconductor laser diode 11 that outputs laser light having a wavelength of 480 [nm] or more and 550 [nm] or less will be described with reference to FIG.

The group III nitride semiconductor laser diode 11 includes a group III nitride substrate 13, an n-type cladding layer 15 provided on the group III nitride substrate 13, and an active layer 17 provided on the n-type cladding layer 15. And a p-type cladding layer 19 provided on the active layer 17. III-nitride substrate 13 is made of hexagonal semiconductor _{In S Al T Ga 1-S} -T N (0 ≦ S ≦ 1,0 ≦ T ≦ 1,0 ≦ S + T ≦ 1), for example, be composed of GaN or the like Can do. Group III nitride substrate 13 has semipolar main surface 13a and back surface 13b. The c-axis Cx of the group III nitride crystal is inclined with respect to the main surface 13a, and more preferably in the m-axis direction of the group III nitride crystal. The n-type cladding layer 15 is made of an n-type (first conductivity type) group III nitride containing Al, and can be made of, for example, AlGaN, InAlGaN, or the like. The n-type cladding layer 15 is the first cladding layer in the present embodiment. The p-type cladding layer 19 is made of a p-type (second conductivity type) group III nitride containing Al, and can be made of, for example, AlGaN, InAlGaN, or the like. The p-type cladding layer 19 is the second cladding layer in the present embodiment.

  The active layer 17 may be a single layer or may have a quantum well structure. If required, the quantum well structure can include alternating well layers and barrier layers. FIG. 1B is an enlarged view showing a part of the configuration of the active layer 17 having such a quantum well structure. The active layer 17 includes a well layer 17a, an intermediate layer 17b, and a barrier layer 17c. The well layer 17a can be made of InGaN or the like, and the barrier layer 17c can be made of InGaN or GaN having a larger band gap energy than the well layer 17a. The intermediate layer 17b can be made of InGaN or GaN having a larger band gap energy than the well layer 17a. Since the intermediate layer 17b is interposed between the well layer 17a and the barrier layer 17c, the threshold voltage or drive voltage of the group III nitride semiconductor laser diode 11 can be lowered.

  In one embodiment, the thickness of the well layer 17a is, for example, 3 [nm], the thickness of the intermediate layer 17b is, for example, 1.1 [nm], and the thickness of the barrier layer 17c is, for example, 13.9 [nm]. The number of well layers 17a can be three, for example. The emission wavelength of the active layer 17 is controlled by the band gap, the In composition, the thickness, and the like of the well layer 17a. The active layer 17 can be provided so as to generate light having a wavelength in the range of 480 [nm] to 550 [nm].

  The group III nitride semiconductor laser diode 11 further includes a first light guide layer 21 between the n-type cladding layer 15 and the active layer 17. The group III nitride semiconductor laser diode 11 further includes a second light guide layer 23 between the active layer 17 and the p-type cladding layer 19. The first light guide layer 21 and the second light guide layer 23 are provided to confine light in the vicinity of the active layer 17 without letting light escape to the group III nitride substrate 13 and reduce the threshold current.

  Referring to FIG. 1, the first light guide layer 21, the active layer 17, and the second light guide layer 23 are arranged on the main surface 13 a of the group III nitride substrate 13 along the normal axis Nx. The inclination angle of main surface 13a of group III nitride substrate 13 is defined by angle ALPHA formed by normal vector NV indicating normal axis Nx and c-axis vector VC indicating the c-axis direction. This angle ALPHA can be in the range of 10 degrees or more and less than 90 degrees with respect to a reference plane Rx (that is, {0001} plane or {000-1} plane) orthogonal to the c-axis of the group III nitride, or It can be in the range of greater than 90 degrees and less than or equal to 170 degrees. The group III nitride substrate 13 can be, for example, GaN, and this angular range can provide the semipolar nature of GaN. Furthermore, the inclination angle ALPHA is preferably in the range of 63 degrees or more and less than 80 degrees, or preferably in the range of more than 100 degrees and 117 degrees or less. According to this angle range, an InGaN layer having an In composition suitable for the active layer 17 for generating light having a long wavelength of 500 [nm] can be provided.

The first light guide layer 21 includes a first layer 31 made of In _x1 Ga _1-x1 N (0 ≦ x1 <1) and a second layer made of In _x2 Ga _1-x2 N (x1 <x2 <1). Layer 33. The first layer 31 is provided on the n-type cladding layer 15, and the second layer 33 is provided between the first layer 31 and the active layer 17. The In composition x2 of the second layer 33 is larger than the In composition x1 of the first layer 31 and smaller than the In composition of the InGaN well layer in the active layer 17. In one embodiment, the first layer 31 can be made of n-type GaN and the second layer 33 can be made of undoped InGaN.

The second light guide layer 23 includes a first layer 35 made of In _x1 Ga _1-x1 N (0 ≦ x1 <1) and a second layer made of In _x2 Ga _1-x2 N (x1 <x2 <1). Layer 37. The first layer 35 is provided on the active layer 17, and the second layer 37 is provided between the active layer 17 and the first layer 35. The In composition x2 of the second layer 37 is larger than the In composition x1 of the first layer 35 and smaller than the In composition of the InGaN well layer in the active layer 17. In one embodiment, the first layer 35 is made of p-type GaN, and the second layer 37 is made of undoped or p-type InGaN.

  The total thickness of the first layer 31 and the second layer 33 and the total thickness of the first layer 35 and the second layer 37 are 0.1 [μm] in order to obtain a stable oscillation mode. It is set to be larger than 0.5 [μm] in order to increase the optical confinement coefficient (Γwell) and realize laser oscillation suitably.

  The In composition x2 of the second layers 33 and 37 preferably satisfies 0.01 ≦ x2 ≦ 0.1. When the In composition x2 is 0.01 or more, a sufficient refractive index can be secured, the optical confinement coefficient (Γwell) can be increased, and laser oscillation can be suitably realized. Further, when the In composition is 0.1 or less, the crystal quality of the active layer 17 can be maintained high, and the light emission efficiency can be improved.

The group III nitride semiconductor laser diode 11 further includes an electron block layer 27. The electron blocking layer 27 is provided so as to divide the second light guide layer 23 into two in the layer thickness direction. In the present embodiment, the electron blocking layer 27 is provided so as to divide the second layer 37 into two in the layer thickness direction. Yes. Specifically, the second layer 37 is divided into a lower layer portion 37 a and an upper layer portion 37 b, the lower layer portion 37 a is provided on the active layer 17, and the upper layer portion 37 b is between the lower layer portion 37 a and the first layer 35. Is provided. The electron block layer 27 is provided between the lower layer portion 37a and the upper layer portion 37b. In one embodiment, the lower layer portion 37a can be made of undoped InGaN, and the upper layer portion 37b can be made of p-type InGaN. The electron block layer 27 can be made of, for example, Al _z Ga _1-z N (0 <z <1), and the Al composition z of the Al _z Ga _1-z N is larger than the Al composition of the p-type cladding layer 19. Moreover, it is preferable that the space | interval (thickness of the lower layer part 37a in this embodiment) of the electronic block layer 27 and the active layer 17 is 50 [nm] or more.

  In the group III nitride semiconductor laser diode 11, the first layer 31, 35 and the upper layer portion 37b of the second layer 37 are n-type or p-type, whereas the second layer 33 and the second layer The lower layer portion 37a of 37 is undoped. Thus, since the second layer 33 and the lower layer portion 37a adjacent to the active layer 17 are undoped, light absorption by the dopant can be avoided. However, these layers 33 and 37a may be doped in order to reduce the resistance for the purpose of driving a low operating voltage. Since the respective dopants are added to the first layers 31, 35 and the upper layer portion 37b, the resistance of these layers 31, 35, 37b can be lowered.

  Group III nitride semiconductor laser diode 11 further includes a p-type contact layer 41 provided on p-type cladding layer 19. The p-type contact layer 41 can be made of, for example, GaN, AlGaN, or the like. The anode electrode 45 a is in contact with the p-type contact layer 41 through the opening of the insulating film 47. The cathode electrode 45 b is in contact with the back surface 13 b of the group III nitride substrate 13.

  In a preferred embodiment, the n-type cladding layer 15 has a thickness of 2000 [nm] and an Al composition of 0.04. The thickness of the first layer 31 of the first light guide layer 21 is 100 [nm], and the In composition x1 is 0 (that is, GaN). The thickness of the second layer 33 is 115 [nm], and the In composition x2 is 0.02. The thickness of the first layer 35 of the second light guide layer 23 is 100 [nm], and the In composition x1 is 0 (that is, GaN). The thicknesses of the lower layer portion 37a and the upper layer portion 37b of the second layer 37 of the second light guide layer 23 are 65 [nm] and 50 [nm], respectively, and the In composition x2 is 0.02. The thickness of the electron block layer 27 is 20 [nm], and the Al composition z is 0.18. The p-type cladding layer 19 has a thickness of 400 [nm] and an Al composition of 0.06. The thickness of the p-type contact layer 41 is 50 [nm]. The anode electrode 45a is made of Ni / Au, and the cathode electrode 45b is made of Ti / Al / Au. In this embodiment, the oscillation wavelength is 497 [nm] and the threshold current is 1.4 [A].

  In another preferred embodiment, the thickness and composition of the n-type cladding layer 15, the electron blocking layer 27, the p-type cladding layer 19, and the p-type contact layer 41 are the same as described above. The thicknesses of the first layer 31 of the first light guide layer 21 and the first layer 35 of the second light guide layer 23 are both 250 [nm], and the In composition x1 is the same as described above. The thicknesses of the second layer 33 of the first light guide layer 21 and the second layer 37 of the second light guide layer 23 are the same as described above, and their In composition x2 is 0.03. In this embodiment, the oscillation wavelength is 520 [nm], and the threshold current is 4 [A].

The group III nitride semiconductor laser diode 11 having the above configuration is manufactured, for example, by the following method. First, a wafer to be a group III nitride substrate 13 is prepared. The main surface of this wafer has a semipolar surface. Next, an n-type Al _0.04 GaN layer to be the n-type cladding layer 15, an n-type GaN layer to be the first layer 31 of the first light guide layer 21, undoped _{an in} 0.02 GaN layer serving as the layer 33, InGaN multiple quantum well layer to be the active layer 17, an undoped _{an in} 0.02 GaN layer serving as the lower layer portion 37a of the second layer 37 of the second optical guide layer 23, The p-type Al _0.18 GaN layer to be the electron blocking layer 27, the p-type In _0.02 GaN layer to be the upper layer portion 37b of the second layer 37 of the second light guide layer 23, and the second light guide layer 23 of the second light guide layer 23 A p-type GaN layer to be the first layer 35, a p-type Al _0.06 GaN layer to be the p-type cladding layer 19, and a p ⁺ -type GaN layer to be the contact layer 41 are sequentially grown on the wafer.

Note that trimethylgallium (TMGa), trimethylaluminum (TMAl), trimethylindium (TMIn), and ammonia (NH ₃ ) can be used as a base material supply gas for the growth of these semiconductor layers. Silane and biscyclopentadienyl magnesium can be used as n-type and p-type dopants. FIG. 2 shows the growth temperature [° C.], the growth rate [Å / min], the flow rate of TMGa [μmol / min], the flow rate of TMIn [μmol / min], the flow rate of TMAl [μmol / Minute] and NH ₃ flow rate [slm (standard liters / minute)].

  The operation and effect of the group III nitride semiconductor laser diode 11 according to this embodiment will be described. In a group III nitride semiconductor laser diode having an oscillation wavelength of 480 [nm] or more and 550 [nm] or less, the refractive index is relatively high in order to obtain a stable oscillation mode by strongly confining light near the active layer. It is effective to use InGaN for the light guide layer. However, when the thickness of the light guide layer containing InGaN is increased, there is a problem that the crystal quality of the active layer is significantly deteriorated as described in the section “Problems to be solved by the invention”.

  Therefore, in the group III nitride semiconductor laser diode 11 of the present embodiment, the first light guide layer 21 includes the first layer 31 and the second layer 33, and the second light guide layer 23 is the first layer. A layer 35 and a second layer 37 are included. The In composition x2 of the second layers 33 and 37 located on the active layer 17 side is higher than the In composition x1 of the first layers 31 and 35. As described above, by providing two layers having different In compositions in the first light guide layer 21 and the second light guide layer 23, the light is transmitted by the second layers 33 and 37 having a high In composition in the vicinity of the active layer 17. It is possible to increase the thickness of the light guide layers 21 and 23 while strengthening the confinement action and suppressing the deterioration of the crystal quality of the active layer 17 by the first layers 31 and 35 having a low In composition. Therefore, a stable oscillation mode can be obtained by the light guide layers 21 and 23 having a thickness larger than 0.1 [μm]. In addition, this effect is particularly remarkable when a group III nitride substrate 13 having a semipolar main surface is used.

  In the present embodiment, the first light guide layer 21 is provided between the n-type cladding layer 15 and the active layer 17, and the second light guide layer 23 is provided between the active layer 17 and the p-type cladding layer 19. Even if the light guide layer is provided only between one of the n-type cladding layer 15 and the active layer 17 and between the active layer 17 and the p-type cladding layer 19. The above effects can be achieved.

  Here, whether or not good laser oscillation can be obtained by changing the In composition x2 and the thickness of the second layers 33 and 37 of the light guide layers 21 and 23 (whether or not the light emission efficiency is sufficient) is experimentally determined. The results of the investigation will be described. FIG. 3 is a graph showing the results, and the vertical axis indicates the thickness of the second layers 33 and 37 (in the case of the second layer 37, the sum of the thicknesses of the lower layer portion 37a and the upper layer portion 37b). The horizontal axis indicates the In composition x2 of the second layers 33 and 37. Further, in the figure, ◯ indicates that good laser oscillation was obtained, and X indicates that good laser oscillation was not obtained. In this experiment, the thickness of the first layers 31 and 35 is 100 [nm].

の関係（図３における直線Ａ）を満たすことによって、また、更に好ましくは

の関係を満たすことによって、活性層１７の結晶品質の低下を効果的に抑制し、十分な発光効率が得られることが示された。 As shown in FIG. 3, when the In composition x2 of the second layers 33 and 37 is 0.04, good laser oscillation was obtained when the thickness was 65 [nm], but the thickness was 115. In the case of [nm], the crystal quality of the active layer 17 was impaired, and good laser oscillation could not be obtained. Further, when the In composition x2 is 0.03, good laser oscillation was obtained even when the thickness was 115 [nm]. However, when the thickness was 165 [nm], good laser oscillation was obtained. It was not obtained. Further, when the In composition x2 is 0.02, good laser oscillation was obtained even when the thickness was 165 [nm], but when the thickness was 215 [nm], good laser oscillation was obtained. It was not obtained. From this result, the thickness d2 [nm] of the second layers 33 and 37 is

And more preferably, by satisfying the relationship (straight line A in FIG. 3)

By satisfying this relationship, it was shown that the crystal quality of the active layer 17 is effectively suppressed from being lowered and sufficient luminous efficiency can be obtained.

  Further, as in the present embodiment, the group III nitride semiconductor laser diode 11 preferably includes an electron block layer 27 provided so as to divide the second light guide layer 23 into two in the layer thickness direction. The distance between the electron blocking layer 27 and the active layer 17 is preferably 50 [nm] or more.

  In group III nitride semiconductor laser diode 11, main surface 13a of group III nitride substrate 13 is a semipolar surface. In a laser diode structure formed on a semipolar plane (particularly on a semipolar plane where the piezoelectric field is negative), the effective band offset of the conductor between the active layer and the electron blocking layer increases. Electrons hardly leak to the p-type semiconductor side. Therefore, the distance between the electron blocking layer 27 and the active layer 17 can be widened to 50 [nm] or more, which is difficult on the c-plane or the nonpolar plane (m-plane). Thereby, it is possible to prevent the light emission characteristics from being deteriorated due to the electron blocking layer 27 distorting the active layer 17. Further, by widening the distance between the electron block layer 27 and the active layer 17 to 50 [nm] or more, the shift of the electric field distribution toward the n-type semiconductor side can be prevented, and the oscillation threshold can be effectively reduced.

Further, as in the present embodiment, the main surface of the group III nitride substrate 13 is preferably inclined in the m-axis direction of the In _S Al _T Ga _1- TN crystal. Thereby, the incorporation efficiency of In when growing the light guide layers 21 and 23 and the active layer 17 is increased, and as a result, good light emission characteristics can be obtained.

(Second Embodiment)
Subsequently, a group III nitride semiconductor laser diode according to a second embodiment of the present invention will be described. FIG. 4 is a drawing schematically showing the structure of the group III nitride semiconductor laser diode 12 according to the present embodiment. This group III nitride semiconductor laser diode 12 is also of a gain guide type that outputs laser light having a wavelength of 480 [nm] or more and 550 [nm] or less as in the first embodiment.

  The group III nitride semiconductor laser diode 12 is provided on the group III nitride substrate 13, an n-type cladding layer (first cladding layer) 15 provided on the group III nitride substrate 13, and the n-type cladding layer 15. And the p-type cladding layer (second cladding layer) 19 provided on the active layer 17. Further, the group III nitride semiconductor laser diode 12 includes a first light guide layer 21 between the n-type cladding layer 15 and the active layer 17. Since the configurations of the group III nitride substrate 13, the n-type cladding layer 15, the active layer 17, the p-type cladding layer 19, and the first light guide layer 21 are the same as those in the first embodiment, their detailed description is omitted. The group III nitride semiconductor laser diode 12 includes a p-type contact layer 41 provided on the p-type cladding layer 19, and the anode electrode 45 a contacts the p-type contact layer 41 through the opening of the insulating film 47. The third embodiment is the same as the first embodiment in that the cathode electrode 45b is in contact with the back surface 13b of the group III nitride substrate 13.

  The group III nitride semiconductor laser diode 12 of this embodiment includes a second light guide layer 25 between the active layer 17 and the p-type cladding layer 19. The second light guide layer 25 is provided in order to confine light in the vicinity of the active layer 17 without letting light escape to the group III nitride substrate 13 and reduce the threshold current.

The second light guide layer 25 includes a first layer 35 made of In _x1 Ga _1-x1 N (0 ≦ x1 <1) and a second layer made of In _x2 Ga _1-x2 N (x1 <x2 <1). Layer 39. The first layer 35 is provided on the active layer 17, and the second layer 39 is provided between the active layer 17 and the first layer 35. The In composition x2 of the second layer 39 is larger than the In composition x1 of the first layer 35 and smaller than the In composition of the InGaN well layer in the active layer 17. In one embodiment, the first layer 35 is made of p-type GaN and the second layer 39 is made of undoped InGaN.

  The total thickness of the first layer 35 and the second layer 39 is set to be larger than 0.1 [μm] in order to obtain a stable oscillation mode, and the laser oscillation is performed by increasing the optical confinement coefficient (Γwell). Is preferably set smaller than 0.5 [μm].

  The In composition x2 of the second layer 39 preferably satisfies 0.01 ≦ x2 ≦ 0.1. When the In composition x2 is 0.01 or more, a sufficient refractive index is ensured, the optical confinement coefficient (Γwell) is increased, and laser oscillation can be suitably realized. Further, when the In composition is 0.1 or less, the crystal quality of the active layer 17 can be maintained high, and the light emission efficiency can be improved.

The group III nitride semiconductor laser diode 12 further includes an electron block layer 29. The electron blocking layer 29 is provided so as to divide the second light guide layer 25 into two in the layer thickness direction. In the present embodiment, the electron blocking layer 29 is provided between the first layer 35 and the second layer 39. Yes. The electron block layer 29 can be made of, for example, Al _z Ga _1-z N (0 <z <1), and the Al composition z of the Al _z Ga _1-z N is larger than the Al composition of the p-type cladding layer 19. The distance between the electron blocking layer 29 and the active layer 17 (the thickness of the second layer 39 in this embodiment) is preferably 50 [nm] or more.

  The difference between the preferred embodiment and the first embodiment is that the thickness of the second layer 33 of the first light guide layer 21 is 65 [nm], and the In composition x2 is 0.03. The thickness of the second layer 39 of the second light guide layer 25 is 65 [nm], and the In composition x2 is 0.03. In this embodiment, the oscillation wavelength is 520 [nm].

  In the group III nitride semiconductor laser diode 12 of the present embodiment, the first light guide layer 21 includes the first layer 31 and the second layer 33, and the second light guide layer 25 is the first layer 35. And a second layer 39. The In composition x2 of the second layers 33 and 39 located on the active layer 17 side is higher than the In composition x1 of the first layers 31 and 35. Thereby, in the vicinity of the active layer 17, the light confinement action is strengthened by the second layers 33 and 39 having a high In composition, and the crystal quality of the active layer 17 is lowered by the first layers 31 and 35 having a low In composition. The thickness of the light guide layers 21 and 23 can be increased while suppressing. Therefore, a stable oscillation mode can be obtained by the light guide layers 21 and 23 having a thickness larger than 0.1 [μm]. In addition, this effect is particularly noticeable when a group III nitride substrate 13 having a semipolar main surface is used.

  Also in this embodiment, the first light guide layer 21 is provided between the n-type cladding layer 15 and the active layer 17, and the second light guide layer is provided between the active layer 17 and the p-type cladding layer 19. 25 is provided when the light guide layer is provided only between one of the n-type cladding layer 15 and the active layer 17 and between the active layer 17 and the p-type cladding layer 19. However, the above effects can be achieved.

  Here, the thickness of the second layers 33 and 39 of the light guide layers 21 and 23 is constant (65 [nm]), and the thickness of the first layers 31 and 35 is changed, whereby the light guide layer 21 is changed. , 25, the result of calculating the optical confinement coefficient Γwell will be described. FIG. 5 is a graph showing the results. The vertical axis represents the optical confinement coefficient Γwell [%], and the horizontal axis represents the thickness [nm] of the light guide layers 21 and 25. In addition, the points plotted in the figure indicate the values of the optical confinement coefficient Γwell obtained by calculation, and the curve B indicates the approximate curve. The oscillation wavelength of this group III nitride semiconductor laser diode 12 is 520 [nm].

  As shown in FIG. 5, the optical confinement coefficient Γwell decreases as the thickness of the light guide layers 21 and 25 increases. When the thickness of the light guide layers 21 and 25 is 0.1 [μm] or less, the light confinement coefficient Γwell is high, but light leaks to the group III nitride substrate 13 and a stable oscillation mode can be obtained. Can not. On the other hand, when the thickness of the light guide layers 21 and 25 is 0.5 [μm] or more, the optical confinement coefficient Γwell is less than 2 [%], and it becomes difficult to obtain good laser oscillation. From this, it is understood that the thickness of the light guide layers 21 and 25 is preferably larger than 0.1 [μm] and smaller than 0.5 [μm].

  6 to 8 are graphs showing the distribution of the guided light when the thickness of the light guide layers 21 and 25 is changed and the oscillation wavelength is changed as described above. 6 to 8, the vertical axis indicates the light intensity. The horizontal axis indicates the position in the thickness direction of the group III nitride semiconductor laser diode 12, the section C1 indicates the range of the optical waveguide layer (the light guide layers 21, 25 and the active layer 17), and the section C2 indicates The range of the group III nitride substrate 13 is shown. 6A to 6C show the case where the thickness of the optical waveguide layer is 390 [nm], and FIGS. 7A to 7C show the thickness of the optical waveguide layer. Is 490 [nm], and FIGS. 8A to 8C show the case where the thickness of the optical waveguide layer is 590 [nm]. FIGS. 6A, 7A, and 8A show the case where the oscillation wavelength is 480 [nm], and FIGS. 6B, 7B, and 8 are shown. (B) shows the case where the oscillation wavelength is 500 [nm], and FIGS. 6 (c), 7 (c) and 8 (c) show the case where the oscillation wavelength is 520 [nm]. Show.

  When the thickness of the optical waveguide layer is 390 [nm] and relatively thin, when the oscillation wavelength becomes a long wavelength of 500 [nm] or longer, as shown in FIG. 6B and FIG. The light is not confined in the light source and the oscillation mode is stabilized in the group III nitride substrate 13 (section C2). However, at an oscillation wavelength of 480 [nm], as shown in FIG. ) Can effectively confine light. At this time, the optical confinement coefficient Γwell was 3.10.

  Further, when the thickness of the optical waveguide layer is 490 [nm], when the oscillation wavelength is 520 [nm] or more, the oscillation mode is generated in the group III nitride substrate 13 (section C2) as shown in FIG. However, when the oscillation wavelength is 500 [nm] or less, the light can be effectively confined in the optical waveguide layer (section C1) as shown in FIGS. 7 (a) and 7 (b). The optical confinement coefficient Γwell at this time was 2.94 (wavelength 480 [nm]) and 2.74 (wavelength 500 [nm]).

  Further, when the thickness of the optical waveguide layer is 590 [nm], the optical waveguide layer is used in the oscillation wavelength range of 480 [nm] to 520 [nm] as shown in FIGS. 8 (a) to 8 (c). Light can be effectively confined inside (section C1). At this time, the optical confinement coefficient Γwell was 2.82 (wavelength 480 [nm]), 2.62 (wavelength 500 [nm]), and 2.45 (wavelength 480 [nm]).

  From the above results, as the oscillation wavelength becomes longer, light leaks from the optical waveguide layer and the oscillation mode tends to be stabilized in the group III nitride substrate 13. It became clear that the oscillation mode can be easily stabilized in the optical waveguide layer by increasing the thickness of the light guide layers 21 and 25 and the active layer 17.

  DESCRIPTION OF SYMBOLS 11, 12 ... Group III nitride semiconductor laser diode, 13 ... Group III nitride substrate, 15 ... N-type clad layer, 17 ... Active layer, 17a ... Well layer, 17b ... Intermediate layer, 17c ... Barrier layer, 19 ... p Mold cladding layer, 21 ... first light guide layer, 23, 25 ... second light guide layer, 27, 29 ... electron blocking layer, 31, 35 ... first layer, 33, 37, 39 ... second layer, 37a ... Lower layer portion, 37b ... Upper layer portion, 41 ... P-type contact layer, 45a ... Anode electrode, 45b ... Cathode electrode, 47 ... Insulating film, ALPHA ... Inclination angle, Cx ... c-axis, NV ... Normal vector, Nx ... Normal axis, Rx ... reference plane, VC ... c-axis vector.

Claims (10)

A group III nitride semiconductor laser diode that outputs laser light having a wavelength of 480 [nm] or more and 550 [nm] or less,
A group III nitride substrate having a semipolar principal surface;
A first conductivity type first cladding layer provided on the group III nitride substrate and made of group III nitride containing Al; and
An active layer provided on the first cladding layer;
A second cladding layer of a second conductivity type provided on the active layer and made of a group III nitride containing Al; and
A light guide layer provided between at least one of the first clad layer and the active layer and between the second clad layer and the active layer;
The light guide layer is
A first layer made of In _x1 Ga _1-x1 N (0 ≦ x1 <1);
A second layer provided between the first layer and the active layer and made of In _x2 Ga _1-x2 N (x1 <x2 <1);
A group III nitride semiconductor laser diode, wherein a total thickness of the first and second layers is greater than 0.1 [μm]. The light guide layer is provided at least between the second cladding layer and the active layer;
The electron blocking layer provided to divide the light guide layer provided between the second cladding layer and the active layer into two in the layer thickness direction, further comprising: Group III nitride semiconductor laser diode.   The group III nitride semiconductor laser diode according to claim 2, wherein a distance between the electron blocking layer and the active layer is 50 nm or more.   4. The group III nitride semiconductor laser diode according to claim 1, wherein a total thickness of the first and second layers is smaller than 0.5 [μm]. 5.   The group III nitride semiconductor laser diode according to claim 1, wherein an In composition x2 of the second layer satisfies 0.01 ≦ x2 ≦ 0.1. The thickness d2 [nm] of the second layer is

The group III nitride semiconductor laser diode according to claim 1, wherein the following relationship is satisfied. The group III nitride substrate is composed of _{In S Al T Ga 1-S} -T N (0 ≦ S ≦ 1,0 ≦ T ≦ 1,0 ≦ S + T ≦ 1),
The primary surface of the group III nitride substrate, the angle of the _{In S Al T Ga 1-S} -T N {0001} plane or the {000-1} range of less than 10 degrees than 90 degrees the surface as a reference crystal The group III nitride semiconductor laser diode according to claim 1, wherein the group III nitride semiconductor laser diode is inclined at Wherein the primary surface of the group III nitride substrate, the angle of the _{In S Al T Ga 1-S} -T N {0001} plane or the {000-1} range of less than 80 degrees 63 degrees or more relative to the surface of the crystal The group III nitride semiconductor laser diode according to claim 7, wherein the group III nitride semiconductor laser diode is inclined at   The group III nitride semiconductor laser diode according to claim 7 or 8, wherein the group III nitride substrate is made of GaN. Wherein the primary surface of the group III nitride substrate is inclined in the m-axis direction of the _{In S Al T Ga 1-S} -T N crystal, in any one of claims 7 to 9 The group III nitride semiconductor laser diode described.

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